1. Field of the Invention
The present invention relates to a method of racemization of optically active tetrahydrofuran-2-carboxylic acid of the formula: ##STR1## wherein the asterisk (*) indicates that the carbon atom with the mark is asymmetric.
2. State of the Art
There are two optically active isomers in tetrahydrofuran-2-carboxylic acid. Among them, (+)-isomer is useful as the sidechain intermediate for producing antibiotics of penem series, and obtained by optical resolution of tetrahydrofuran-2-carboxylic acid which is industrially produced as a racemate. The optical resolution of this compound was first achieved by Belanger et al (Can. J. Chem. 61, 1383 (1983)). The method, however, uses expensive brucine and ephedrine as the resolving agent.
It is advantageous to racemize the antipode remaining after one of the optically avtive isomers is separated by resolution, and to reuse the racemate in by further optical resolution. Therefore, it has been desired to establish the racemization technology. However, there has not been known an efficient way of racemizing optically active tetrahydrofuran-2-carboxylic acid. Among various carboxylic acids, some, e.g., amino acids can be racemized by heating in an alkaline medium. The method is, however, far from practical use, because of a very low rate of racemization when applied in tetrahydrofuran-2-carboxylic acid.